The present application relates to a method of treating pain states with reduced side effects resulting from a therapeutic use of a CB2 cannabinoid receptor agonist comprising a combination therapy consisting of a CB2 cannabinoid receptor agonist in an amount effective to obtain a therapeutic effect, and a CB1 cannabinoid receptor ligand to the subject in an amount effective to block the adverse effects but not to antagonize the therapeutic effect of the cannabinoid receptor agonist.
(−)-Δ9-Tetrahydrocannabinol (Δ9-THC), the major psychoactive constituent of marijuana, exerts a broad range of biological effects through its interactions with two cannabinoid (CB) receptor subtypes, CB1 and CB2. CB1 receptors are highly expressed in the central nervous system and to a lesser degree in the periphery in a variety of tissues of the cardiovascular and gastrointestinal systems. By contrast, CB2 receptors are most abundantly expressed in multiple lymphoid organs and cells of the immune system, including spleen, thymus, tonsils, bone marrow, pancreas and mast cells.
The psychotropic effects caused by Δ9-THC and other nonselective CB agonists are mediated by CB1 receptors. Activation of the CB1 receptor by administration of a CB1 agonist produces a number of undesirable physiological and behavioral effects. In the central nervous system, activation of the CB1 receptor can result in a variety of psychotropic effects such as euphoria, sedation, catalepsy, paranoia, panic and anxiety. CB1 activation also negatively impacts cognitive function, leading to a loss of short-term memory, poor executive function and impaired learning. CB1 activation also produces physiological effects that manifest themselves outside the central nervous system such as hypothermia, increased heart rate, decreased blood pressure, and dry mouth. The undesirable effects mediated by CB1 activation may negatively impact the usefulness to a patient of any medication that displays some ability to activate the CB1 receptor. The undesirable effects resulting from activation of the CB1 receptor with a CB1 agonist may be blocked, inhibited, or prevented by administration of a selective CB1 antagonist or inverse agonist.
Several lines of evidence support the assertion that CB2 receptors play a role in analgesia. For example, Zimmer et al. have reported that the nonselective cannabinoid agonist Δ9-THC retains some analgesic efficacy in CB1 receptor knockout mice (Zimmer, A., et al., Proc. Nat. Acad. Sci., 1999, 96, 5780-5785). HU-308 is one of the first highly selective CB2 agonists identified that elicits an antinociceptive response in the rat formalin model of persistent pain (Hanus, L., et al., Proc. Nat. Acad. Sci., 1999, 96, 14228-14233). The CB2-selective cannabiniod ligand AM-1241 exhibits robust analgesic efficacy in animal models of acute thermal pain (Malan, T. P., et al., Pain, 2001, 93, 239-245; Ibrahim, M. M., et al., Proc. Nat. Acad. Sci., 2005, 102(8), 3093-3098), persistent pain (Hohmann, A. G., et al., J. Pharmacol. Exp. Ther., 2004, 308, 446-453), inflammatory pain (Nackley, A. G., et al., Neuroscience, 2003, 119, 747-757; Quartilho, A. et al., Anesthesiology, 2003, 99, 955-60), and neuropathic pain (Ibrahim, M. M., et al., Proc. Nat. Acad. Sci., 2003, 100, 10529-10533). The CB2-selective partial agonist GW405833, also known as L768242, is efficacious in rodent models of neuropathic, incisional, and both chronic and acute inflammatory pain (Valenzano, K. J., et al., Neuropharmacology, 2005, 48, 658-672 and Clayton, N., et al., Pain, 2002, 96, 253-260). The analgesic effects induced by these CB2-selective ligands are blocked by CB2 and not by CB1 receptor antagonists.
CB2 receptors are present in tissues and cell types associated with immune functions and CB2 receptor mRNA is expressed by human B cells, natural killer cells, monocytes, neutrophils, and T cells (Galiegue et al., Eur. J. Biochem., 1995, 232, 54-61). Studies with CB2 knockout mice have suggested a role for CB2 receptors in modulating the immune system (Buckley, N. E., et al., Eur. J. Pharmacol. 2000, 396, 141-149). Although immune cell development and differentiation are similar in knockout and wild type animals, the immunosuppressive effects of Δ9-THC are absent in the CB2 receptor knockout mice, providing evidence for the involvement of CB2 receptors in immunomodulation. As such, selective CB2 agonists may be useful for the treatment of autoimmune diseases including but not limited to multiple sclerosis, rheumatoid arthritis, systemic lupus, myasthenia gravis, type I diabetes, irritable bowel syndrome, psoriasis, psoriatic arthritis, and hepatitis; and immune related disorders including but not limited to tissue rejection in organ transplants, gluten-sensitive enteropathy (Celiac disease), asthma, chronic obstructive pulmonary disease, emphysema, bronchitis, acute respiratory distress syndrome, allergies, allergic rhinitis, dermatitis, and Sjogren's syndrome.
Microglial cells are considered to be the immune cells of the central nervous system (CNS) where they regulate the initiation and progression of immune responses. They are quiescent and resting having a ramified morphology as long as the CNS is healthy. Microglia express a variety of receptors enabling them to survey the CNS and respond to pathological events. Insult or injury to the CNS leads to microglial cell activation, which is characterized by various morphological changes allowing response to the lesion. Ramifications are retracted and microglia are transformed into amoeboid-like cells with phagocytic function. They can proliferate, rapidly migrate to the site of injury, and produce and release cytokines, chemokines and complement components (Watkins L. R., et al., Trends in Neuroscience, 2001, 24(8), 450; Kreutzberg, G. W., Trends Neurosci., 1996, 19, 312-318). CB2 receptor expression on microglia is dependent upon inflammatory state with higher levels of CB2 found in primed, proliferating, and migrating microglia relative to resting or fully activated microglial (Carlisle, S. J., et al. Int. Immunopharmacol., 2002, 2, 69). Neuroinflammation induces many changes in microglia cell morphology and there is an upregulation of CB2 receptors and other components of the endocannabinoid system. It is conceivable that CB2 receptors may be more susceptible to pharmacological effects during neuroinflammation (Walter, L., Stella, N., Br. J. Pharmacol. 2004, 141, 775-785). Neuroinflammation occurs in several neurodegenerative diseases, and induction of microglial CB2 receptors has been observed (Carrier, E. J., et al., Current Drug Targets—CNS & Neurological Disorders, 2005, 4, 657-665). Thus, CB2 ligands may be clinically useful for the treatment of neuroinflammation.
CB2 receptor expression has been detected in perivascular microglial cells within normal, healthy human cerebellum (Nunez, E., et al., Synapse, 2004, 58, 208-213). Perivascular cells are immunoregulatory cells located adjacent to CNS blood vessels and, along with parenchymal microglia and astrocytes, they play a pivotal role in maintaining CNS homeostasis and blood-brain barrier functionality (Williams, K., et al., Glia, 2001, 36, 156-164). CB2 receptor expression has also been detected on cerebromicrovascular endothelial cells, which represent a main component of the blood-brain barrier (Golech, S. A., et al., Mol. Brain. Res., 2004, 132, 87-92). A recent report demonstrated that CB2 receptor expression is up-regulated in the brains of macaques with simian immunodeficiency virus-induced encephalitis (Benito, C., et al., J. Neurosci. 2005, 25(10), 2530-2536). Thus, compounds that affect CB2 signaling may protect the blood-brain barrier and be clinically useful in the treatment of neuroinflammation and a variety of neuroinflammatory disorders including retroviral encephalitis, which occurs with human immunodeficiency virus (HIV) infection in the CNS.
Multiple sclerosis is common immune-mediated disease of the CNS in which the ability of neurons to conduct impulses becomes impaired through demyelination and axonal damage. The demyelination occurs as a consequence of chronic inflammation and ultimately leads to a broad range of clinical symptoms that fluctuate unpredictably and generally worsen with age. These include painful muscle spasms, tremor, ataxia, motor weakness, sphincter dysfunction, and difficulty speaking (Pertwee, R. G., Pharmacol. Ther. 2002, 95, 165-174). The CB2 receptor is up-regulated on activated microglial cells during experimental autoimmune encephalomyelitis (EAE) (Maresz, K., et al., J. Neurochem. 2005, 95, 437-445). CB2 receptor activation prevents the recruitment of inflammatory cells such as leukocytes into the CNS (Ni, X., et al., Multiple Sclerosis, 2004, 10, 158-164) and plays a protective role in experimental, progressive demyelination (Arevalo-Martin, A.; et al., J. Neurosci., 2003, 23(7), 2511-2516), which are critical features in the development of multiple sclerosis. Thus, CB2 receptor agonists may provide a unique treatment for demyelinating pathologies.
Alzheimer's disease is a chronic neurodegenerative disorder accounting for the most common form of elderly dementia. Recent studies have revealed that CB2 receptor expression is upregulated in neuritic plaque-associated microglia from brains of Alzheimer's disease patients (Benito, C., et al., J. Neurosci., 2003, 23(35), 11136-11141). In vitro, treatment with the CB2 agonist JWH-133 abrogated β-amyloid-induced microglial activation and neurotoxicity, effects that can be blocked by the CB2 antagonist SR144528 (Ramirez, B. G., et al., J. Neurosci. 2005, 25(8), 1904-1913). CB2 agonists possessing both anti-inflammatory and neuroprotective actions thus may have clinical utility in treating neuroinflammation and in providing neuroprotection associated with the development of Alzheimer's disease.
Increased levels of epithelial CB2 receptor expression are observed in human inflammatory bowel disease tissue (Wright, K., et al., Gastroenterology, 2005, 129, 437-453). Activation of CB2 receptors re-established normal gastrointestinal transit after endotoxic inflammation was induced in rats (Mathison, R., et al., Br. J. Pharmacol. 2004, 142, 1247-1254). CB2 receptor activation in a human colonic epithelial cell line inhibited TNF-α-induced interleukin-8 (IL-8) release (Ihenetu, K. et al., Eur. J. Pharmacol. 2003, 458, 207-215). Chemokines released from the epithelium, such as the neutrophil chemoattractant IL-8, are upregulated in inflammatory bowel disease (Warhurst, A. C., et al., Gut, 1998, 42, 208-213). Thus, administration of CB2 receptor agonists represents a novel approach for the treatment of inflammation and disorders of the gastrointestinal tract including but not limited to inflammatory bowel disease, irritable bowel syndrome, secretory diarrhea, ulcerative colitis, Crohn's disease and gastroesophageal reflux disease (GERD).
Hepatic fibrosis occurs as a response to chronic liver injury and ultimately leads to cirrhosis, which is a major worldwide health issue due to the severe accompanying complications of portal hypertension, liver failure, and hepatocellular carcinoma (Lotersztajn, S., et al., Annu. Rev. Pharmacol. Toxicol., 2005, 45, 605-628). Although CB2 receptors were not detectable in normal human liver, CB2 receptors were expressed liver biopsy specimens from patients with cirrhosis. Activation of CB2 receptors in cultured hepatic myofibroblasts produced potent antifibrogenic effects (Julien, B., et al., Gastroenterology, 2005, 128, 742-755). In addition, CB2 knockout mice developed enhanced liver fibrosis after chronic administration of carbon tetrachloride relative to wild-type mice. Administration of CB2 receptor agonists represents a unique approach for the treatment of liver fibrosis.
CB2 receptors are involved in the neuroprotective and anti-inflammatory mechanisms induced by the interleukin-1 receptor antagonist (IL-1ra) (Molina-Holgado, F., et al., J. Neurosci., 2003, 23(16), 6470-6474). IL-1ra is an important anti-inflammatory cytokine that protects against ischemic, excitotoxic, and traumatic brain insults. CB2 receptors play a role in mediating these neuroprotective effects indicating that CB2 agonists may be useful in the treatment of traumatic brain injury, stroke, and in mitigating brain damage.
Cough is a dominant and persistent symptom of many inflammatory lung diseases, including asthma, chronic obstructive pulmonary disease, viral infections, and pulmonary fibrosis (Patel, H. J., et al., Brit. J. Pharmacol., 2003, 140, 261-268). Recent studies have provided evidence for the existence of neuronal CB2 receptors in the airways, and have demonstrated a role for CB2 receptor activation in cough suppression (Patel, H. J., et al., Brit. J. Pharmacol., 2003, 140, 261-268 and Yoshihara, S., et al., Am. J. Respir. Crit. Care Med., 2004, 170, 941-946). Both exogenous and endogenous cannabinoid ligands inhibit the activation of C-fibers via CB2 receptors and reduce neurogenic inflammatory reactions in airway tissues (Yoshihara, S., et al., J. Pharmacol. Sci. 2005, 98(1), 77-82; Yoshihara, S., et al., Allergy and Immunology, 2005, 138, 80-87). Thus, CB2-selective agonists may have utility as antitussive agents for the treatment of pulmonary inflammation, chronic cough, and a variety of airway inflammatory diseases including but not limited to asthma, chronic obstructive pulmonary disease, and pulmonary fibrosis.
Artherosclerosis is a chronic inflammatory disease and is a leading cause of heart disease and stroke. CB2 receptors have been detected in both human and mouse atherosclerotic plaques. Administration of low doses of THC in apolipoprotein E knockout mice slowed the progression of atherosclerotic lesions, and these effects were inhibited by the CB2-selective antagonist SR144528 (Steffens, S., et al., Nature, 2005, 434, 782-786). Thus, compounds with activity at the CB2 receptor may be clinically useful for the treatment of atherosclerosis.
CB2 receptors are expressed on malignant cells of the immune system and targeting CB2 receptors to induce apoptosis may constitute a novel approach to treating malignancies of the immune system. Selective CB2 agonists induce regression of malignant gliomas (Sanchez, C., et al., Cancer Res., 2001, 61, 5784-5789), skin carcinomas (Casanova, M. L., et al., J. Clin. Invest., 2003, 111, 43-50), and lymphomas (McKallip, R. J., et al., Blood, 2002, 15(2), 637-634). Thus, CB2 agonists may have utility as anticancer agents against tumors of immune origin.
In view of this evidence, compounds that are selective agonists for the CB2 receptor over the CB1 receptor are potential therapeutic agents for the treatment of a variety of disorders including inflammatory pain, inflammatory disorders, immune disorders, neurological disorders, neurodegeneration, cancer, respiratory disorders, cardiovascular disorders, osteoporosis, obesity, and diabetes.
Pain alleviation occurs at doses of a CB2 selective agonist that do not cause or may to a very limited extent cause undesirable effects associated with CB1 receptor activation. At higher doses, however, drug concentrations of a CB2 selective agonist may reach sufficiently high levels so as to begin to activate CB1 receptors, due to some residual weak CB1 activity of the CB2 selective agent producing ataxia and catalepsy (Valenzano et al., Neuropharmacology, Vol. 48 pages 658-672, 2005). Therefore, at higher doses CB2 selective agonists may begin to display the aforementioned undesirable effects due to residual CB1 activation.
In view of the aforementioned evidence, a combination therapy co-administering a CB2 selective agonist and a CB1 selective antagonist or inverse agonist can provide the therapeutic benefit of alleviating pain through activation of CB2 receptors while concomitantly preventing the undesirable adverse effects due to the residual weak activation of the CB1 receptor. This combination therapy provides a safer, more tolerable and more effective method of treating pain, or any other disorder mediated through CB2 receptors, with reduced incidence of abuse liability.